Adaptive subdivision ocean modifier
Unfortunately, adaptive subdivision (at least as it is now) works by applying the subdivision to the UV dynamically with respect to the view.  It must be dynamic.  However, the ocean modifier obviously radically changes geometry and it does so by modifying a known geometry.  With ASD, the geometry is unknown and is in flux.  For this reason, ASD must be applied last.

This is just a workaround and it may not even be applicable to your needs (and you've probably already thought of it).  It's not adaptive but you can lock the camera to plane and maybe make it appear as if your subject is moving through the ocean.

Create a plane and subdivide it in sections:



Apply Ocean mod Set Geometry to Displace.  Play with settings:





Sorry for the crummy sky hdri: